9mm vs 38 pressure

[Wheeljack]

Pressure confuses me. A 9mm round may be at 30000PSI, a .357 at 40000PSi and the 38Spec at 16000. If I load a 38 into a 357 revolver, can't I load the 38 to a pressure of 40000? Is the only reason 38's are loaded so low is because the gun may be very old? If I bought a new S&W revolver in 38 spec. is it made lighter so it would only be safe with a 16000PSI round? It's almost as if the gun you buy should state the pressure it was built for. Are there any good resourses that explain these questions?

[Sarge]

Generally 38's say they can handle +P if they can. Gun might be light but the cylinder would be strong enough to take it.

[Guy Neill]

It's not so much that they are made lighter as much as the steel alloy may be different, and/or the heat treatment differs. It's not rated for the higher pressure based on the strength of the material.

Each cartridge has a specified maximum pressure and the guns are designed around that pressure. The pressure limitation is marked on the gun in the form of the chambered cartridge. Many reloading manuals will state the maximum pressure, or an older copy of the SAAMI specifications for cartridges is availalbe on the SAAMI website.

Guy

[Justsomeguy]

Well... the cases are also a factor. Some 38spcl cases are of the "balloon head" variety and will not stand up to pressures any higher than the spec for the cartridge. If you don't want your hands peppered with brass you might want to limit pressure in .38 cases. Using cut down 357 brass has been tried, but then...

The guns are another matter, but like others have said it is not necessarily the steel or weight of the gun. Guns marked as 38 Special are only designed and proofed for the 38 cartridge, and there are no guarantees for anything more than that.